Fragility of Polymer Nanocomposites with Ideal Nanoparticle Dispersion

We investigate the impact of the addition of nanoparticles (NP) on the fragility of a model glass forming polymer melt by molecular dynamics simulation. We first consider a fixed density path and find that the fragility changes, like the change in the glass transition temperature, follow directly from the attractive or repulsive polymer-NP interactions. We further show how the fragility can be connected with local vibrational changes, quantified by the Debye-Waller factor. We contrast these results with those we obtain along a path of fixed pressure, more experimentally relevant. For the isobaric case, we find changes in packing can have a larger effect on fragility than surface effects due only to NP interactions at fixed system density.